Rep. Franks resigned on Dec. 8, 2017, over #MeToo sexual harassment accusations.
Governor Doug Ducey (R-AZ) set the date for the primary as Feb. 27, and the special election date is set for April 24, 2018.
(AZ law requires a special election because Rep. Franks resigned more than 6 months before the next scheduled election in Nov. 2018).
Debbie Lesko (R) won the April 24 special election.

Rep. Becerra resigned after being appointed as California Attorney General to succeed Senator-elect Kamala Harris. Becerra called the appointment by Gov. Jerry Brown a "phenomenal opportunity" but it leaves his constituents unrepresented for months and then burdened by the expense of a Special Election (April 4 with a June 6 runoff).
On April 4, Robert Lee Ahn was defeated in special Democratic primary election. On June 6, Jimmy Gomez defeated William Rodriguez Morrison (R).

Targeted by BOTH the NRCC and the DCCC: Incumbent targeted by NRCC Patriot Program to defend the House GOP majority. Democratic challenger targeted by DCCC's Red to Blue program: former Army Ranger Jason Crow

Withdrew retirement: Rep. Perlmutter announced his retirement on April 9, 2017 to enter the CO Governor 2018 race. On Aug. 21, 2017, he withdrew from the gubernatorial race and re-entered the House race.

Targeted by BOTH the NRCC and the DCCC: Incumbent targeted by NRCC Patriot Program to defend the House GOP majority. Democratic challenger targeted by DCCC's Red to Blue program: St. Clair County State's Attorney Brendan Kelly

Targeted by BOTH the NRCC and the DCCC: Incumbent targeted by NRCC Patriot Program to defend the House GOP majority.
Democratic challenger targeted by DCCC's Red to Blue program: state Rep. Abby Finkenauer

Targeted by BOTH the NRCC and the DCCC: Incumbent targeted by NRCC Patriot Program to defend the House GOP majority.
Democratic challenger targeted by DCCC's Red to Blue program: former Defense official Elissa Slotkin

Rep. Conyers resigned on Dec. 5, 2017, over #MeToo sexual harassment accusations.
Governor Rick Snyder (R-MI) opted to keep the House seat vacant for 11 months, until Nov. 2018.
(MI law allows for a special election anytime between now and the next election; Snyder chose the special election date to coincide with the general election date in Nov. 2018);
Special election Democratic challenger: Brenda Jones; General election Democratic challenger: Rashida Tlaib

Targeted by BOTH the NRCC and the DCCC: Incumbent targeted by NRCC Patriot Program to defend the House GOP majority.
Democratic challenger targeted by DCCC's Red to Blue program: 2016 nominee Angie Craig

Targeted by BOTH the NRCC and the DCCC: Incumbent targeted by NRCC Patriot Program to defend the House GOP majority.
Democratic challenger targeted by DCCC's Red to Blue program: state Assemblyman Anthony Brindisi

Special election: Rep. Louise Slaughter passed away on March 16, 2018. Gov. Andrew Cuomo must call a special election by July 1st; on April 19, a lawsuit was filed to enforce that deadline, but the special election will be held on Nov. 6.
Challengers: Jim Maxwell (Republican) vs. Joe Morelle (Democratic)

Hot Race: Rep. Collins suspended his re-election campaign on Aug. 11, 2018, after being arrested and indicted for insider trading. Collins plans to serve out his term "to support President Trump's agenda"; he is "retiring" but his name will still appear on the ballot in November. Challenger: Nate McMurray (Democratic)

Rep. Tiberi resigned on Oct. 19, 2017, effective Jan. 31, 2018, to take a job with the Ohio Business Roundtable, leaving his constituents unrepresented, and then requiring taxpayers to foot the bill for a special election to replace him.
Governor John Kasich (R-OH) set the special election date for August 7th, following a primary election on May 8th 2018.
The winner of the August 2018 special election will serve until January 2019, and all current candidates are ALSO running for the regular election in November 2018 (the winner of the November 2018 election will serve from Jan.2019 until Jan.2021).
Contenders include Franklin County Sheriff Zach Scott (D) and 2016 Congressional nominee Ed Albertson (D), vs. State Sen. Troy Balderson (R) and State Senator Kevin Bacon (R)

Rep. Bridenstine was appointed as Administrator of NASA in September, 2017.
Upon confirmation in April 2018, he decided to NOT resign from Congress, but announced he would not run for re-election in 2018.
Challengers: Tim Gilpin (Democratic) vs. Kevin Hern (Republican)

Rep. Meehan resigned on April 27, 2018 over #MeToo sexual misconduct charges.
Governor Tom Wolf (D-PA) set the date for the special election to coincide with the November general election.
Due to court-ordered redistricting, the new 7th district has different boundaries than Meehan's existing 7th district.
Contenders for new 7th district: Susan Wild (D) vs. Marty Nothstein (R)

Rep. Murphy resigned on Oct. 5, 2017 over #MeToo sexual misconduct charges, effective Oct. 21.
Governor Tom Wolf (D-PA) set the date for the special election for March 13, 2018.
Republicans nominated State Rep. Rick Saccone on Nov. 11; on Nov. 19 Democrats nominated Conor Lamb, who won the March 13 special election.

Special election: Incumbent Rep. Farenthold resigned April 6th, 2018, amid a #MeToo sexual harrassment scandal. Gov. Greg Abbott has called a special election for June 30, with a runoff (if needed) in September.
Republican-leaning district favors Michael Cloud

Rep. Chaffetz resigned effective June 30, 2017, saying he never intended "a lifetime career" in Congress, choosing instead a job at Fox News, only a few months into a 2-year term. His resignation leaves his constituents unrepresented for months and then burdened by the expense of a Special Election.
It was scheduled by Gov. Gary Herbert for Nov. 7 2017; the winner was John Curtis.